James Cameron has called Donald Trump a “madman” and criticised the Republican presidential candidate over his denial of climate change, according to the Associated Press.

The Avatar director, speaking ahead of the premiere of his new documentary short, Not Reality TV, at the Democratic national convention, said that Trump’s assertion that he would tear up the Paris climate agreement and his repeated dismissal of the science behind climate change was “incredibly reckless and dangerous”.

Cameron’s film, introduced at the DNC by Sigourney Weaver, who provided the voiceover, details how US workers have been affected by droughts and adverse weather in recent years. “Crops are failing, food prices are rising, our children are at risk,” says Weaver, before a victim of Hurricane Sandy describes how she lost her daughter to the storm.

Sigourney Weaver introduces James Cameron’s film at the Democratic national convention. Photograph: ddp USA/Rex Shutterstock

The film features well-known figures including Jack Black, Don Cheadle and the Pope, who is shown describing a planet teetering on the brink of “suicide”. Hillary Clinton makes a late cameo, but the starring role is saved for Trump himself, who is shown at various rallies ridiculing the idea of climate change. “We need some global warming,” he says at one point. “It’s freezing!”

In a statement, Cameron said: “We made this film to show the reality of climate change – how it’s directly affecting millions of people each day. As I’ve said before, to save our planet we need to mobilise like we did during the second world war – the threat to our country and children is that severe.”

“As an American, I am also deeply concerned about my family’s future, about our shared future as a nation,” said Weaver in her introduction to the documentary. “That future is at risk.”